European commissioners, the continent’s regulators, have been criticised by their own watchdog for refusing to divulge details of meetings they and their staff have held with lobbyists.

The European ombudsman, who polices European Union institutions, said the Commission was “wrongly blanking out the names of industry lobbyists” in documents released to the public, in defiance of 2001 rules.

The ombudsman’s comments came in a case concerning Peter Mandelson, the trade commissioner, but the criticism applies across the Commission.

Mr Mandelson’s spokesman said he was guided by the Commission’s legal service on releasing names: “We operate an open-door policy and intend to continue to do so. We seek contact with the widest possible range of interests.”

Nikiforos Diamandouros, the ombudsman, said: “The practice of systematically blanking out names of lobbyists is wrong ... The public interest should overrule any potential wish for secrecy by the lobby groups and their representatives.”

The Commission claims data protection rules prevent it from publishing the names of people meeting commissioners.

The ombudsman upheld a complaint from Corporate Europe Observatory, an Amsterdam-based transparency campaigner, which has asked for records of meetings between Mr Mandelson and representatives of business groups lobbying on trade issues.

The ombudsman is authorised to seek redress for the complaint. If unsuccessful, he can propose a resolution to the European parliament. However, he said he would suspend judgment until the European Court of Justice had examined three pending cases on the same theme.

A Commission spokeswoman said it would await the court’s judgment before commenting.